AU2010305355A1 - Automated radiosynthesis - Google Patents

Abstract

The present invention provides a method to obtain radiofluorinated compounds useful for in vivo imaging GABA receptors. The method of the invention is high-yielding and may conveniently be carried out on an automated synthesizer such as Fastlab. A further aspect of the invention is a cassette suitable for carrying out the automated method of synthesis of the invention. Novel precursor compounds useful in the method of the invention are also provided, as are a number of novel compounds obtained by the method of the invention.

Description

WO 2011/042529 PCT/EP2010/065077 AUTOMATED RADIOSYNTHESIS Technical Field of the Invention The present invention relates to in vivo imaging and in particular to in vivo imaging of gamma-aminobutyric acid (GABA) receptors of the central nervous 5 system (CNS). The invention provides a method suitable for the automated synthesis of radiofluorinated GABA receptor antagonist compounds. Description of Related Art Gamma-aminobutyric acid (GABA) is the most important inhibitory neurotransmitter in the human brain. GABA receptors are transmembrane 10 receptors and fall into two main types, GABAA receptors and GABAB receptors. GABAA receptors have been the major focus of pharmacological development to date. Many GABAA receptor subtypes have been discovered and novel chemical structures have been developed which are selective for these subtypes. Normal activation of the GABAA receptor results in chloride ion 15 being selectively conducted through its pore. This chloride channel gating is generally inhibitory on a neuron by virtue of stabilising the membrane potential near to resting level. Defective GABAA receptor neurotransmission may be caused by a reduction in GABAA receptors, or by defective functioning of the GABAA receptor due to e.g. 20 a genetic mutation in a GABAA receptor gene, traumatic brain injury, or a pharmacological insult, and is implicated in a number of neurological and psychiatric disorders, including epilepsy, anxiety disorders, Parkinson's disease and chronic pain. The development of radioligands selective for the GABAA receptor is therefore of value in terms of brain imaging studies in living 25 human patients, in particular those suffering from disorders associated with defective GABAA receptor neurotransmission. Flumazenil (also known as flumazepil, code name Ro 15-1788, trade names Anexate, Lanexat, Mazicon, Romazicon) is an imidazo[1,5 -1- WO 2011/042529 PCT/EP2010/065077 a][1,4]benzodiazepine that is a neutralising allosteric modulator of GABAA receptors in the CNS (Johnston 1996 Pharmacol Ther; 69(3): 173-198). The most common use of flumazenil to date has been as an antidote to benzodiazepine overdose as it reverses the effects of benzodiazepines by 5 competitive inhibition at the benzodiazepine binding site of the GABAA receptor. In addition, because flumazenil has little or no agonist activity, radiolabelled versions thereof have been developed as positron emission tomography (PET) radiotracers. [48F]FMZ has the same chemical formula as flumazenil but wherein 18F is 10 incorporated by direct radiofluorination of a nitro precursor: 0 0 [K/K2.2.2]1/ 18

F

0 2 N N F N 0 0

[

18 F]Flumazenil [8 F]FMZ binds to the GABAA receptor with high affinity (Ki around 0.5nM) and selectivity. Ryzhikov et al (2005 Nuc Med Biol; 32: 109-116) describe the preparation of [1 F]FMZ from a nitro precursor compound. This synthesis, 15 however, has been found by the present inventors to have a less than optimal end of synthesis (EOS) yield of 2.7-7.7% (described herein as a comparative example). These EOS yields are comparable to those reported by Odano et al (Neuroimage 2009; 45(3): 891-902). The present invention seeks means to obtain radiofluorinated agents that bind 20 to the GABAA receptor with high affinity in improved yields compared to the prior art methods. Summary of the Invention The present invention provides a method to obtain radiofluorinated compounds useful for in vivo imaging GABAA receptors. The method of the invention is -2- WO 2011/042529 PCT/EP2010/065077 high-yielding in comparison to the prior art methods. A further aspect of the invention is a cassette suitable for carrying out the automated method of synthesis of the invention. Novel precursor compounds useful in the method of the invention are also provided, as are certain novel radiofluorinated 5 compounds obtained by the method of the invention. Detailed Description of the Invention In one aspect, the present invention provides a method to obtain a compound of Formula I: N R3 N R1 N R2 R O (I) 10 wherein: one of R1 and R2 is 1F and the other is hydrogen; and,

R

3 is a C3-5 heterocycle; or, R 3 is C(=O)-O-R 4 wherein R 4 is hydrogen, or a straight- or branched-chain C1-4 alkyl; wherein said method comprises: 15 (i) providing a precursor compound of Formula la: N R13 N _12 R 0 (Ia) wherein: -3- WO 2011/042529 PCT/EP2010/065077 one of R" and R is a leaving group and the other is hydrogen, wherein: when R" is said leaving group it is selected from tri-C 1

.

3 alkyl ammonium or -I*-Ar, wherein Ar is phenyl substituted with one or more R groups, wherein R is selected from hydrogen, nitro, cyano, halogen, C 1

.

1 ohydroxyalkyl, C2-10 5 carboxyalkyl, C1.10 alkyl, C2-10 alkoxyalkyl, C1.1o hydroxyalkyl, C1.10 aminoalkyl, Cl1 haloalkyl, C614 aryl, C312 heteroaryl, C3-20 alkylaryl, C2-10 alkenyl, and C2-10 alkynyl; and, when R 1 2 is said leaving group it is selected from nitro, tri-C 1

.

3 alkyl ammonium or -I*-Ar, wherein Ar is as defined above for R 11 ; and, 10 R13 is as defined for R3 of Formula I; and, (ii) reacting said precursor compound with a suitable source of [1 F]Fluoride. A "precursor compound" comprises a non-radioactive derivative of a radiolabelled compound, designed so that chemical reaction with a convenient chemical form of the detectable label occurs site-specifically; can be conducted 15 in the minimum number of steps (ideally a single step); and without the need for significant purification (ideally no further purification), to give the desired in vivo imaging agent. Such precursor compounds are synthetic and can conveniently be obtained in good chemical purity. The precursor compound may optionally comprise a protecting group for certain functional groups of the 20 precursor compound. A "leaving aroup" is a substituent of the precursor compound as defined above which is replaced with 18F when the precursor compound is reacted with a suitable source of [1 F]fluoride, thereby permitting incorporation of 18F site specifically to result in the desired radiofluorinated compound of Formula 1. 25 By the term "protecting group" is meant a group which inhibits or suppresses undesirable chemical reactions, but which is designed to be sufficiently reactive that it may be cleaved from the functional group in question under mild enough conditions that do not modify the rest of the molecule. After -4- WO 2011/042529 PCT/EP2010/065077 deprotection the desired product is obtained. Protecting groups are well known to those skilled in the art and are suitably chosen from, for amine groups: Boc (where Boc is tert-butyloxycarbonyl), Fmoc (where Fmoc is fluorenylmethoxycarbonyl), trifluoroacetyl, allyloxycarbonyl, Dde [i.e. 1-(4,4 5 dimethyl-2,6-dioxocyclohexylidene)ethyl] or Npys (i.e. 3-nitro-2-pyridine sulfenyl); and for carboxyl groups: methyl ester, tert-butyl ester or benzyl ester. For hydroxyl groups, suitable protecting groups are: methyl, ethyl or tert-butyl; alkoxymethyl or alkoxyethyl; benzyl; acetyl; benzoyl; trityl (Trt) or trialkylsilyl such as tetrabutyldimethylsilyl. The use of further protecting groups are 10 described in 'Protective Groups in Organic Synthesis', Theorodora W. Greene and Peter G. M. Wuts, (Third Edition, John Wiley & Sons, 1999). The term "alkjy" used either alone or as part of another group is defined herein as any straight, branched or cyclic, saturated or unsaturated CnH 2 n.

1 group. The term "ryI" used either alone or as part of another group is defined herein 15 as any C6-14 molecular fragment or group which is derived from a monocyclic or polycyclic aromatic hydrocarbon, or a monocyclic or polycyclic heteroaromatic hydrocarbon. The term halogenn" means a group selected from fluorine, chlorine, bromine, and iodine. 20 The term "nitro" refers to the group -NO 2 . The term "cyano" refers to the group -CN. The term "carboxyalkyl" refers to an alkyl group as defined above substituted with at least one -COOH. The term "alkoxyalkyl" refers to an alkyl ether radical wherein the term alkyl is 25 as defined above. The term "hydroxyalkyl" refers to an alkyl radical as defined above wherein at least one hydrogen atom has been replaced by an -OH group. -5- WO 2011/042529 PCT/EP2010/065077 The term "aminoalkyl" refers to an alkyl radical as defined above wherein at least one hydrogen atom has been replaced by an -NH 2 group. The term "haloalkyl" refers to an alkyl radical as defined above wherein at least one hydrogen atom has been replaced by a halogen wherein halogen is as 5 defined herein. The term "heteroaryl" refers to an aryl as defined above wherein at least one carbon atom is replaced with a heteroatom selected from 0, N and S. The term "alkylaryl" refers to an alkyl radical as defined above in which at least one hydrogen atom is replaced by an aryl radical as defined above. 10 The term "heterocycle" refers herein to an aliphatic or aromatic cyclic radical wherein the cycle comprises one or more heteroatoms selected from nitrogen, oxygen or sulfur. The term "alkenyl" means a straight-chain or branched-chain hydrocarbon radical having one or more double bonds. 15 The term "alkynyl" means a straight-chain or branched chain hydrocarbon radical having one or more triple bonds. In a preferred embodiment of the method of the invention where R' is 18 F, R" is trimethyl ammonium or -I*-Ar. In a most preferred embodiment of the method of the invention R2 is 1F. When R2 20 is 1F, it is preferred that R is nitro, trimethyl ammonium or -I*-Ar. When R2 is 1F, it is most preferred that R is nitro.

R

3 of Formula I and R 13 of Formula la are the same and are preferably C(=O)-O

R

4 , wherein R 4 is straight or branched-chain C1-4 alkyl, preferably methyl, ethyl, isopropyl or tert-butyl. R 4 is most preferably ethyl, isopropyl or tert-butyl, and 25 especially preferably ethyl. The reaction scheme disclosed by Yang et al (2009 Synthesis; 6: 1036-1040) -6- WO 2011/042529 PCT/EP2010/065077 can be adapted to obtain precursor compounds of Formula Ia wherein R"' is a leaving group. Scheme 1 illustrates how the precursor compounds can be obtained: H RHH tihgsarcosine/DMSO R- 1OH R~hsgn 0 0 a b H 0N 13 O gN R Diethyl phosphochloridate N 21 / (i) (ii) tButOK, THF (iii) 0 N, N- R 13 0 N RD C d Scheme 1 5 In Scheme 1, where R" is trialkylammonium, R21 is NO 2 , and where R" is an iodonium salt, R21 is bromine. R is as defined for Formula Ia. The appropriate amino benzoic acid compound a, equipped to perform the required chemistry to introduce the desired leaving group at later stage, is reacted with triphosgene to afford the benzoxazine-2,4-dione intermediate b. Reaction of b 10 with sarcosine in DMSO yields the benzodiazepine c. At this stage, where R 1 ' is trialkylammonium, R21 of compound c is converted to trialkylammonium in step (i) before carrying out step (ii)to obtain compound d. Where R 1 ' is an iodonoim salt, R 21 is converted to the iodonium salt in step (iii) after carrying out step (ii). 15 Where R is the leaving group, Scheme 2 may be used to obtain the precursor compound: -7- WO 2011/042529 PCT/EP2010/065077

NH

2 0 H H 0 2 1N 0 DMSO N S2OH NCO R O H R O e f g Diethyl phosphorochloridate R 1 3 tButOK, THE 0)_______ (ii) (i N C N 1R31 Scheme 2 h R is as defined for R in Scheme 1 above. Compound e is obtained from commercially-available 2,6-dinitro benzoic acid starting material by standard chemical transformations. Compound e is treated as described for compound 5 a of Scheme 1 to give the benzodiazepine intermediate g, which in turn is transformed in the desired imidazobenzodiazepine either before (i.e. (ii) and then (iii)) or after (i.e. (i) and then (ii)) introducing the desired leaving group. Steps (i)-(iii) are as described above in relation to Scheme 1. [48F]Fluoride is typically obtained as an aqueous solution which is a product of the 10 irradiation of an [18O]-water target. It has been widespread practice to carry out various steps in order to convert [1 F]Fluoride into a reactive nucleophilic reagent, such that it is suitable for use in nucleophilic radiolabelling reactions. These steps include the elimination of water from [1 F]-fluoride ion and the provision of a suitable counterion (Handbook of Radiopharmaceuticals 2003 Welch & Redvanly 15 eds. ch. 6 pp 195-227). Nucleophilic radiofluorination reactions are then carried out using anhydrous solvents (Aigbirhio et al1995 J Fluor Chem; 70: 279-87). In order to increase the reactivity of fluoride and to avoid hydroxylated by-products resulting from the presence of water, water is typically removed from [ 1F]Fluoride prior to the reaction and the radiofluorination reactions are carried out using 20 anhydrous reaction solvents (Aigbirhio et al1995 J Fluor Chem; 70: 279-87). The removal of water from the [1 F]Fluoride is referred to as making "naked" [48F]Fluoride. This is regarded in the prior art relating to nucleophilic fluoridation as a step necessary to increase the reactivity of fluoride as well as to avoid -8- WO 2011/042529 PCT/EP2010/065077 hydroxylated by-products resulting from the presence of water (Moughamir et al 1998 Tett Letts; 39: 7305-6). A further step that is used to improve the reactivity of [ 18 F]Fluoride for radiofluoridation reactions is to add a cationic counterion prior to the removal of 5 water. The counterion should possess sufficient solubility within the anhydrous reaction solvent to maintain the solubility of the fluoride ion. Counterions that have been used include large but soft metal ions such as rubidium or caesium, potassium complexed with a cryptand such as Kryptofix

TM

, or tetraalkylammonium salts. A preferred suitable source of [1 F]Fluoride for use in the method of the 10 invention is selected from [1 F] potassium fluoride and [1 F] caesium fluoride. [1 F] potassium fluoride is most preferred, and especially preferably when it is complexed with a cryptand such as KryptofixTM because of its good solubility in anhydrous solvents and enhanced fluoride reactivity. In a preferred embodiment, the method of the invention may further comprise: 15 (iii)removal of excess [1 F]Fluoride; and/or, (iv)removal of any protecting groups; and/or, (v) removal of organic solvent; and/or, (vi)formulation of the resultant compound together with a biocompatible carrier to obtain a radiopharmaceutical composition suitable for mammalian 20 administration. The biocompatiblee carrier" is a fluid, especially a liquid, in which the radiofluorinated compound is suspended or dissolved, such that the radiopharmaceutical composition is physiologically tolerable, i.e. can be administered to the mammalian body without toxicity or undue discomfort. The 25 biocompatible carrier is suitably an injectable carrier liquid such as sterile, pyrogen-free water for injection; an aqueous solution such as saline (which may advantageously be balanced so that the final product for injection is either isotonic or not hypotonic); an aqueous solution of one or more tonicity-adjusting -9- WO 2011/042529 PCT/EP2010/065077 substances (e.g. salts of plasma cations with biocompatible counterions), sugars (e.g. glucose or sucrose), sugar alcohols (e.g. sorbitol or mannitol), glycols (e.g. glycerol), or other non-ionic polyol materials (e.g. polyethyleneglycols, propylene glycols and the like). The biocompatible carrier may also comprise biocompatible 5 organic solvents such as ethanol. Such organic solvents are useful to solubilise more lipophilic compounds or formulations. Preferably the biocompatible carrier is pyrogen-free water for injection, isotonic saline or an aqueous ethanol solution. The pH of the biocompatible carrier for intravenous injection is suitably in the range 4.0 to 10.5. 10 Currently, the synthesis of 18F-labelled compounds, particularly for use as PET tracers, is most conveniently carried out by means of an automated synthesis apparatus, e.g. Tracerlab and Fastlab TM (both GE Healthcare). However, the prior art method is not suitable for automation. In Comparative Example 1 herein it is demonstrated that radioflurination of nitromazenil is not an ideal 15 approach for the automated synthesis of [1 F]FMZ on Fastlab due to the low yield, and also because of the temperature required to obtain effective incorporation of [1 F]fluoride. The existing FASTIab reaction vessel is made of a cyclo-olefin co-polymer (COC) which can be used at temperatures up to 130 0 C. The prior art method used to prepare [1 F]FMZ from a nitro precursor 20 requires a temperatures of around 160 0 C. At these temperatures the COC reaction vessel loses containment. As demonstrated in the experimental examples below, changing the leaving group on the nitromazenil precursor from nitro to trimethylammonium allowed the reaction temperature to be reduced to 1300C whilst maintaining an EOS 25 yield of 7%. Moving the nitro leaving group from the position meta to the amide carbonyl to the position ortho to the amide carbonyl gave an improvement in EOS yield from 2.7-7.7% to 18-23% whilst also reducing the reaction temperature. In a particularly preferred embodiment, the method of the invention is 30 automated. The radiochemistry is performed on the automated synthesis -10- WO 2011/042529 PCT/EP2010/065077 apparatus by fitting a "cassette" to the apparatus. Such a cassette normally includes fluid pathways, a reaction vessel, and ports for receiving reagent vials as well as any solid-phase extraction cartridges used in post-radiosynthetic clean up steps. 5 In a further aspect of the present invention there is provided a cassette for carrying out the automated method of the invention comprising: (i) a vessel containing a precursor compound, wherein said precursor compound is as suitably and preferably defined above; and (ii) means for eluting the vessel with a suitable source of [1 F]Fluoride, 10 wherein said suitable source of [1 F]Fluoride is as suitably and preferably defined above. The cassette may also comprise an ion-exchange cartridge for removal of excess 18F. The reagents, solvents and other consumables required for the automated synthesis may also be included together with a data medium, such 15 as a compact disc carrying software, which allows the automated synthesiser to be operated in a way to meet the end user's requirements for concentration, volumes, time of delivery etc. In another aspect, the present invention provides a compound of Formula I as defined in the method of the invention wherein R' is hydrogen, R2 is [1 F], and R4 20 is ethyl, isopropyl or t-butyl, wherein R 4 is most preferably ethyl. In a yet further aspect, the present invention provides a precursor compound of Formula la is as defined above wherein one of R" and R is trimethylammonium or -I*-Ar, and the other is hydrogen. Preferably, one of R" and R 1 2 is trimethylammonium and the other is hydrogen. Most preferably, R 12 is nitro, 25 trimethylammonium or -I*-Ar, most especially preferably R 1 2 is nitro. R1 is preferably C(=O)-O-R 4 wherein R 4 is ethyl, isopropyl or tert-butyl, and wherein R4 is preferably ethyl. -11- WO 2011/042529 PCT/EP2010/065077 Brief Description of the Examples Comparative Example 1 describes the preparation of [1 F]flumazenil from a nitro precursor compound. Example 2 describes the preparation of [1 F]flumazenil from a 5 trimethylammonium precursor compound. Example 3 describes the preparation of an iodonium salt precursor compound for [1 F]flumazenil. Example 4 describes the preparation of ortho-[1 F]flumazenil from a nitro precusror compound. 10 Example 5 describes the preparation of ortho-[1 F]flumazenil tert-butyl ester from a nitro precursor compound. Example 6 describes the preparation of ortho-[1 F]flumazenil isopropyl ester from a nitro precursor compound. Example 7 describes a method for evaluation of the in vivo biodistribution of 15 ortho-[1 F]flumazenil. List of Abbreviations used in the Examples aq aqueous CIP 2-Chloro-1,3-dimethylimidazolidium hexafluorophosphate DCM dichloromethane 20 DIPEA N,N-Diisopropylethylamine DMF dimethyl formamide DMSO dimethyl sulfoxide EOS end of synthesis -12- WO 2011/042529 PCT/EP2010/065077 Et ethyl g gram(s) h hour(s) HPLC high performance liquid chromatography 5 LCMS liquid chromatography mass spectrometry MeCN acetonitrile min minute(s) mL millilitre(s) mM millimolar 10 mmol millimole(s) mol mole(s) QMA quaternary methylammonium Rf retention factor rt room temperature 15 SPE solid phase extraction TBA tetrabutylammonium TEA triethanolamine THF tetrahydrofuran TLC thin layer chromatography 20 UV ultraviolet -13- WO 2011/042529 PCT/EP2010/065077 Examples Comparative Example 1: Preparation of ( 8 Fflumazenil (f 8 FFMZ)from Nitromazenil Example 1(i): Synthesis of 4-Methyl-7-nitro-3,4-dihvdro-1H 5 benzo[e1,47diazep.)ine-2,5-dione (1) H O N

I

ON N 0 1 Commercially-available 5-Nitroisatoic anhydride (40 g, 0.192 mol) was dissolved in DMSO (50 mL) by stirring and heating the flask slowly to 1400C. Sarcosine (17.1 g, 0.192 mol) was slowly added in portions to the solution. 10 Upon addition, at 1400C, the solution started bubbling (generation of C02). The mixture was left stirring for 2.5 h. The mixture was left to cool and slowly poured on ice cold water in a beaker. The solution was stirred with a glass rod and a yellow solid precipitated out. The solid was separated by filtration and washed several time with water, then dried in vacuum oven at 400C overnight. 15 The yellow solid isolated was identified as the desired product 1 in a 78% yield. 1H NMR (D 6 -DMSO): 5 3.14 (3H, s, NCH 3 ), 3.97 (2H, s, NCH 2 CO), 7.30 (1 H, d, J = 9 Hz, HNCCHCH), 8.33 (1 H, dd, J = 9 and 3 Hz, CHCHCNO 2 CH), 8.33 (1 H, d, J= 3 Hz, OC-CCH), 11.05 (1H, s, NH). 20 -14- WO 2011/042529 PCT/EP2010/065077 Example 1(Ii): Preparation of Nitromazenil (2) N 0 N OEt ON N 2 0 Potassium tert-butoxide (0.6 g, 5 mmol) was added to a solution of intermediate 1 (1 g, 4.3 mmol) in THF (10 mL) and DMF (2 mL) at 00C under 5 nitrogen. After 30 min the reaction was cooled to OC, treated dropwise with diethyl chlorophosphate (0.7 mL, 5 mmol) and stirred for 30 min. Meanwhile to a stirred solution of ethyl isocyanoacetate (0.6 mL, 5 mmol) in THF (10 mL) under nitrogen at 00C was added potassium tert-butoxide (0.6 g, 5 mmol) and stirred for 15 min. This was then added slowly to the mixture of intermediate 1 10 at 00C. This was stirred at 00C for 0.5 h then at room temperature for another 2 h. TLC (ethyl acetate) showed starting material (Rf 0.4) and a new spot (Rf 0.2) by UV and KMnO 4 . The reaction was quenched with acetic acid and left stirring overnight. The reaction mixture was poured into ice/water. This was extracted with ethyl 15 acetate, and the organic layer was washed with water, brine, dried and concentrated to a thick dark dense oil. This was chromatographed on several times using the following conditions: 1) Companion, using DCMI/ethyl acetate (twice) 2) Companion using petrol/ethyl acetate (twice) 20 50 mg of the pure material 2 was obtained as a colourless solid (yield 4%) 1H NMR (CDCI 3 ): 5 1.39 (3H, t, J = 7 Hz, CH3), 3.28 (3H, s, ArCONCH 3 ), 4.37 (2H, q, J= 7 Hz, OCH 2 ), 4.40 (1H, br s, CH2), 5.26 (1H, br s, CH2), 7.60 (1H, d, J= 8.9 Hz, ArCHCHCNO 2 ), 7.94 (1 H, s, NCHN), 8.45 (1 H, dd, J= 8.9 and 2.8 Hz, ArCHCHCNO 2 ), 8.95 (1 H, d, J= 2.5 Hz, ArCHCNO 2 ). -15- WO 2011/042529 PCT/EP2010/065077 Example 1(Iii): Radiofluorination of Nitromazenil (2) to Obtain ( 8 F7 flumazenil

((

8 F FMZ) N O N OEt F N\ [ 1 8 F]FMZ 0 18F labeling was done on a TRACERIab automated synthesis module (GE 5 Healthcare). [1 F] fluoride was trapped on a pre-conditioned QMA cartridge and then transferred to the reaction vessel using a solution of tetra-n-butylammonium bicarbonate in MeCN/water (MeCN 1400 tL, water 100 tL, TBA.HCO 3 27 mg) from vial 1. The solution was dried at 100 C for 10 minutes then 1200C for 20 minutes using nitrogen plus vacuum flow and then cooled to 500C. 10 To the dried [1 F]fluoride was added nitromazenil (18.8 mg) in DMF (1 mL) from vial 3. The reaction mixture was heated at 1600C for 30 min then it was cooled to 500C. The reaction mixture was diluted with 10 mM phosphoric acid (2.5 mL)from vial 5 and was transferred to the crude product tube. The crude product was then transferred onto the preparative HPLC loop manually. 15 Preparative HPLC gave a peak with retention time 17.5 minutes which was cut using into the TRACERIab round bottomed flask containing water (12 mL). The prepartative HPLC system was fitted with a liquid flow scintillation counter. HPLC Column Phenomenex Luna C18(2) 250xlOmm 5 p Solvent A = 10 mM phosphoric acid, B = MeCN, 25% B isocratic Flow rate 4 mL/min UV 254nm Loop 5 mL Sensitivity 2000K The mixture in the round bottom flask was trapped on a tC18 plus lite SPE -16- WO 2011/042529 PCT/EP2010/065077 cartridge (pre conditioned with 1 mL ethanol then 2 mL water). The SPE cartridge was washed with water (3 mL) and the crude product eluted into a P6 vial using EtOH (0.5 mL) and water (4.5 mL). Initial activity 193.8 MBq @11:14 Activity of formulated product 14.8 MBq @12:48 =7.7% end of synthesis yield 5 Example 2: Preparation of ("FIflumazenil (f"F1FMZ)from a Trimethylammonium Precursor Compound Example 2(i): Synthesis of 4-methyl-7-Amino-3,4-dihvdro-1H benzo[e1,47diazep.)ine-2,5-dione (3) H 0 NI H2N 0 3 10 Intermediate 1 (3.48 g, 15 mmol, preparation described in Example 1) was suspended in a 120 mL of 1:1 solution of THF/Ethanol. The suspension was treated with nitrogen followed by vacuum, before adding Pd/C 10% (0.7 g), suspended in ethanol. The reaction vessel was then fitted onto the Parr hydrogenator and left under hydrogen pressure (20 psi) for about 3 hours with 15 stirring. The excess hydrogen gas was removed using vacuum and then nitrogen was purged through the solution. The catalyst was filtered off using celite and the filtrate was evaporated to the minimum amount of ethanol. A white precipitate formed which was separated by filtration and dried under vacuum to afford 918 mg of desired material 3 in 30% yield. 20 1H NMR (DMSO): 5 3.07 (3H, s, NCH 3 ), 3.74 (2H, s, NCH 2 CO), 5.19 (2H, s,

NH

2 ), 6.69 (1 H, dd, J = 8.6 and 2.5 Hz, ArCHCNH 2 ), 6.77 (1 H, d, J = 8.6 Hz, ArCHCNHCO), 6.90 (1 H, d, J = 2.5 Hz, COCCHCNH 2 ), 9.97 (1 H, s, NH). -17- WO 2011/042529 PCT/EP2010/065077 Example 2(i): Synthesis of 4-methyl-7-Dimethylamino-3,4-dihvdro-IH benzo[e1,47diazep.ine-2,5-dione (4) H 0 NJ NN 0 4 To a solution of intermediate 3 (3.0 g, 13 mmol) and 37% aq formaldehyde (21 5 mL, 0.26 mol) in acetonitrile at 00C, NaBH 3 CN (4.8 g, 77 mmol) was added portionwise. The reaction mixture was stirred at 00C for 2 h and then at room temperature for 1 h. Acetic acid (1.4 mL) was then added and the reaction mixture was stirred for another 2 h. The reaction mixture was poured into ethyl ether, washed with 2N KOH and the basic layer was extracted several times 10 with ethyl acetate. The organic phases were collected and dried and solvents removed in vacuum to give an amorphous yellowish solid. Notes: upon addition of acetic acid formation of gas was observed and the reaction was strongly exothermic. The solid obtained was triturated with ethyl acetate, isolated by filtration and 15 washed with diethyl ether to give a pale yellow fluffy solid. Proton NMR confirmed the material to be intermediate 4 (2.97 g, 98%). 1H NMR (DMSO): 5 3.09 (3H, s, NCH 3 ), 3.77 (2H, s, NCH 2 CO), 6.92-6.98 (3H, m, ArCHCN(CH 3

)

2 , ArCHCNHCO, COCCHCN(CH 3

)

2 ), 10.09 (1H, s, NH). 20 Example 2(Ii): Synthesis of Trim eth yl-(4-m eth yl-2,5-dioxo-2,3,4,5-tetrah ydro -18- WO 2011/042529 PCT/EP2010/065077 IH-benzo[ef{1,47diazep.in-7-yl)-ammonium (5) H 0 N* + N 0 5 Intermediate 4 (2.97 g, 13 mmol) was dissolved in DCM (75 mL) and methyl triflate (1.67 mL, 15 mmol) was added at room temperature dropwise under 5 nitrogen flow. Within 1 min a solid started to crash out of solution. After 10 min TLC analysis (ethyl acetate) showed that SM had disappeared. The reaction was therefore stopped. Diethyl ether (20 mL) was added and the solid was isolated by filtration as white sticky material. The reaction afforded intermediate 5 in quantitative yield. 10 1H NMR (DMSO): 5 3.15 (3H, s, CONCH 3 ), 3.61 (9H, s, N'(CH 3

)

3 ), 3.91 (2H, s,

NCH

2 CO), 7.28 (1H, d, J= 9.19 Hz, ArCHCNHCO), 8.10 (1H, dd, J= 3.06 and 9.19 Hz, ArCHCN'(CH 3

)

3 ), 8.25 (1H, d, J= 3.06 Hz, COCCHCN'(CH 3

)

3 ), 10.73 (1H, s, NH). Example 2(iv): Synthesis of the Trimethylammonium Precursor Compound (6) S OEt N ± N 1I 0 15 6 Sodium hydride (240 mg of a 60% dispersion in mineral oil, 6 mmol) was added to a solution of intermediate 5 (2 g, 5 mmol) in THF (15 mL) and DMF (10 mL) at room temperature under nitrogen. After 40 min the reaction was cooled to OC and treated dropwise with diethyl chlorophosphate (1.08 mL, 7.5 mmol) 20 and stirred for 30 min. Meanwhile to a stirred solution of ethyl isocyanoacetate (0.656 mL, 6 mmol) in DMF (6 mL) under nitrogen at 00C was added sodium hydride (280 mg of a 60% dispersion in mineral oil, 7 mmol) and stirred for 15 -19- WO 2011/042529 PCT/EP2010/065077 min. This was then added slowly to the mixture of intermediate 5 at 00C. This was stirred at 00C for 0.5 h then room temperature for 30 mins. LCMS analysis of the crude after this time showed presence of desired mass. The reaction was quenched with acetic acid and worked up. 5 The reaction mixture was poured into ice/water. This was extracted with ethyl acetate, followed by DCM. LCMS analysis of the organics and the water suggested desired material present in the water layer. This was therefore taken to dryness (using rotary evaporation) and then the crude analysed by semiprep HPLC. The desired product 6 was isolated in 25% yield. 10 HPLC conditions: 5-95% methanol/water gradient over 30 mins; Luna 10i C18(2) 250 x 50 mm column. 1H NMR (D 2 0): 5 1.37 (3H, t, J = 7.1 Hz, COOCH 2

CH

3 ), 3.22 (3H, s, NCH 3 ), 3.73 (9H, s, N(CH 3

)

3 ), 4.41 (2H, m, COOCH 2

CH

3 ), 4. (1H, br d, J= 15.3 Hz,

NCH

2 ), 5.13 (1H, br d, J = 15.3 Hz, NCH 2 ), 7.93 (1H, d, J = 9.2 Hz, 15 ArCHCNHCO), 8.25 (1 H, dd, J =9.2 and 3.1 Hz, ArCHCN (CH 3

)

3 ), 8.27 (1 H, s, ArNCHN), 8.40 (1 H, d, J =3.1 Hz, COCCHCN*(CH 3

)

3 ). Example 2(v): Radiofluorination of Trimethylammonium Precursor Compound (6) to Obtain ( 8 Flflumazenil( 18 FLFMZ) N O N OEt F N\ [ 18 F]FMZ 0 20 [ F] fluoride was transferred to a Wheaton vial to which was added TBA.HC0 3 (400 pL). The solution was dried at 110 C under a flow of N 2 (-0.5L/ min) for 30 min, then cooled to room temperature. To the dried [ F] fluoride was added the trimethylammonium precursor (31 mg) in DMSO (1 mL). The reaction mixture was heated at 1300C for 25 min when it -20- WO 2011/042529 PCT/EP2010/065077 was cooled to room temperature. The reaction mixture was transferred from the Wheaton vial into a P6 vial. The Wheaton vial was rinsed with water (1mL) and transferred to the P6 vial, an additional 3mL off ammonium acetate (50mM) was added. The reaction mixture was loaded onto preparative HPLC (Hichrom 5 ACE C5 1 Ox1 00mm column; solvent A = 50mM Ammonium Acetate, solvent B = MeCN; 4mL/min; UV 254nm) for purification. Analytical HPLC (Phenomenex Luna C18(2) 50x2mm column; solvent A = 50mM Ammonium Acetate, solvent B = MeCN; 0.4mL/min; UV 254nm) confirmed that [ F] flumazenil was obtained at 95% radiochemical purity. The 10 end of synthesis yield of [ F]flumazenil using this method was 6%. Example 3: Preparation of an lodonium Salt Precursor Compound for (FFIflumazenil (f"F FMZ) 1) KO t Bu, N H H O diethyl chlorophosphate __/ N0 N 2)KOtBu, N sarcosine, DMSO ethyl isocyanoacetate Br j 75% Br N 30% Br N 7 0 8 0 9 0 Pd(PPh 3 ) HMDT, mW N O N TOAc) 2

F

3 C 0 O 21 1N 15 Commercially available 5-bromoisatoic anhydride (7) was heated in DMSO with sarcosine at 1500C. This afforded intermediate 8 in 75% yield. The annulation afforded intermediate 9 with a yield of 30% using the conditions illustrated in the reaction scheme. Intermediate 9 and hexamethylditin/Pd(PPh 3

)

4 were heated in the microwave at 1300C for 15 minutes to afford the stannane 20 intermediate 10 in 35% yield. The iodonium conversion was obtained using a 1:5 ratio of intermediate 10 and (diacetoxyiodo)benzene, after 24 h at RT the -21- WO 2011/042529 PCT/EP2010/065077 reaction had gone to completion. The desired iodonium salt precursor compound 11 was obtained in 21% yield. Example 4: Preparation of ortho-f 8 Fflumazenil from ortho-Nitromazenil -\ 0 F 0 0 HC N +O DMSO, Cs 2

CO

3 , rt, 12h E~ to N N 0 EtO H NO 2 72% OEt 0 12Ot

NO

2 13 NBS, benzene benzoyl peroxide (cat) quant. hv (60W) 0 EtO N 0 Br MeOH, DIEPA, MeNH 2 N 0 OEt reflux N 61% ~N Ot

NO

2 O 2 14 (not isolated) 5 Example 4(i) Preparation of 2-Fluoro-6-nitro benzoic acid Ethyl Ester (12) 2-Fluoro-6-nitro benzoic acid (1.5 g, 8 mmol) was suspended in DCM (30 mL) under nitrogen flow at 0 C. Oxalyl chloride (1.5 g, 1.06 mL, 12 mmol) was slowly added and the reaction was left stirring overnight. The formation of the 10 acyl chloride could be followed by TLC (ethyl acetate). The solvent was removed in vacuo and the residue was redissolved in DCM (20 mL). Ethanol (0.4 g, 0.5 mL, 8 mmol) was added at 00C with TEA (0.8 g, 1.1 mL, 8 mmol) and the reaction was left stirring at room temperature for 3 hours. After this time a small amount of mixture was analysed by 1H & 19F NMR to show -22- WO 2011/042529 PCT/EP2010/065077 quantitative formation of 12. The reaction mixture was diluted with DCM (20 mL) and washed with water (2 x 50mL). The organic layer was separated, dried over MgSO 4 and filtered. The solvent was removed to dryness to afford a brown oil, which gave white 5 crystals of 12 (1.5 g, 88 %) over time. 1H NMR (300 MHz, CDC1 3 ): 6H 1.39 (3H, t, J = 7.1 Hz, COOCH 2

CH

3 ), 4.47 (2H, q, J = 7.1 Hz, COOCH 2

CH

3 ), 7.47 (1 H, td, J= 8.3 and 1.2 Hz,

NO

2 CCHCHCHCF), 7.59 (1 H, td, J= 8.3 and 5.2 Hz, NO 2 CCHCHCHCF), 7.98 (1 H, dt, J= 8.3 and 0.9 Hz, NO 2 CCHCHCHCF); 19F NMR (282 MHz, CDCI 3 ): EF 10 -112.4. Example 4(ii) Preparation of Intermediate 13 12 (3 g, 0.014 mol) and ethyl 4-methyl-5-imidazole-carboxylate (1.96 g, 0.013 mol) were dissolved in 30 mL of DMSO. Cesium carbonate (4.6 g, 0.014 mol) was added and the mixture was stirred at rt for 3 days. 15 Crude was analysed by LCMS using a 5-95% acetonitrile/water gradient over 3 min. This showed a new species with mass 348.03 in the positive. TLC analysis (Ethyl acetate) showed a new spot with rf 0.4. The reaction mixture was poured into ice water and then extracted with ethyl acetate (xl) followed by DCM (x3). The combined organics were concentrated 20 and liquid loaded on silica column for flash chromatography (details on next page). The product 13 was isolated in 72% yield (3.5 g). 1H NMR (CDCl 3 ): 6 1.19 (6H, t, J= 7.05 Hz, COOOCH 2

CH

3 ), 1.42 (3H, t, J 7.05 Hz, COOCH 2

CH

3 ), 2.37 (3H, s, NCCH 3 ), 4.21 (2H, q, J = 7.05 Hz,

COOCH

2

CH

3 ), 4.41 (2H, q, J = 7.05 Hz, COOCH 2

CH

3 ), 7.49 (1 H, s, NCHN), 25 7.62 (1 H, dd, J = 7.97 Hz, CCHCHCHCNO 2 ), 7.77 (1 H, t, J = 7.97 & 8.27 Hz,

CCHCHCHCNO

2 ), 8.37 (1 H, dd, J = 8.27 Hz, CCHCHCHCNO 2 ). -23- WO 2011/042529 PCT/EP2010/065077 Example 4(i) Preparation of ortho-Nitromazenil (14) To a stirred solution of bromide (4.25g, 0.010 mol) in 50 mL of methanol a solution of DIPEA (2.84g, 3.8 mL, 0.022 mol) and methyl amine (6.5 mL of 2M solution in methanol, 0.013 mol) in methanol (50 mL) was slowly added. The 5 reaction was refluxed overnight. TLC analysis using ethyl acetate showed quantitative conversion of the starting material 13 to two main new spots (rf 0.5 and 0.3). Crude was analysed by LCMS using a 5-95% acetonitrile/water gradient over 3 min. This showed a new species with mass 331.03 in the positive and two other major peaks. The solvent was removed to dryness and 10 the crude was liquid loaded on column for flash chromatography using DCM/Ethyl acetate 1% methanol. LCMS of the 2 major combined fractions showed the desired material in a mixture with two other products. Each fraction was submitted to a second purification using DCM/ethyl acetate. The product 14 was then re-crystallised from both fractions using ethanol. 15 Desired material was isolated pure in 15%yield. 1H NMR (CDC1 3 ) 5 1.43 (3H, s, CH3), 3.20 (3H, s, NCH 3 ), 4.32-4.50 (2H, m,

OCH

2 ), 4.54 (1H, d, J= 16 Hz, NCH), 5.30 (1H, d, J= 16 Hz, NCH'), 7.66 (1H, dd, J = 8 Hz and 1 Hz, NCCH), 7.70 (1 H, dd, J = 8 and 8 Hz, CHCHCH), 7.94 (1 H, dd, J = 8 and 1 Hz,CHCNO 2 ), 7.97 (1 H, s, NCHN). 20 Example 4(iv): Radiofluorination of ortho-Nitromazenil to Obtain ortho [( Flflumazenil Radiofluorination was done on a FASTlab automated synthesis module (GE Healthcare). A cassette was assembled from component parts as follows. An 11 mm vial 25 containing 20.5 mg K222, 140 pl K2CO3 (2.9 mg in water) & 1.06 ml MeCN, a second 11mm vial containing 1.3 ml of precursor solution (6.5 mg precursor 14 in 1.3 ml of dry DMF), a 13 mm vial containing phosphoric acid (2.6 mL, 10 mM), a 13 mm vial containing saline (0.9%, 2.4 mL) and a 13mm vial -24- WO 2011/042529 PCT/EP2010/065077 containing ethanol (4 mL) were inserted into the cassette. A pre-treated QMA cartridge was fitted, and a tC18+ cartridge. The required operating sequence file was uploaded from the control PC into the internal memory of the FASTlab. The cassette was mounted on to the 5 FASTIab synthesizer. The [ F]fluoride vial was pierced using a needle connected to the line to the fluoride inlet on the FASTlab. A clean, empty product collection vial was connected which was pre filled with 0.9% saline (7 mL). The synthesis sequence was then commenced and the FASTIab hardware test step completed. The fluoride was trapped on the QMA cartridge 10 and dried in the reaction vessel. The solution of precursor 14 was added and heated at 1300C for 30 minutes. The reaction mixture was diluted with phosphoric acid (10 mM, 2.2 mL). Once the crude product had transferred to the HPLC loop, the HPLC run was started (see below for details of the preparative HPLC conditions). HPLC Column Phenomenex Prodigy ODS-prep 250x10mm 10 p Solvent A = 10 mM phosphoric acid, B = MeCN, 25% B isocratic Flow rate 4 mL/min UV 254nm Loop 5 mL Sensitivity 200K 15 Once the product had been injected onto the prep HPLC the cut (retention time 13.7 minutes) was performed manually for approximately minute into a vial containing -13 ml water. The diluted cut was drawn back onto the FASTIab for reformulation on the tC1 8 plus cartridge. The amount of radioactivity in 20 formulated product (in 1 mL ethanol and 9 mL saline) was measured in an ion chamber. A sample of product was sub dispensed and posted out of the hot cell for analysis. -25- WO 2011/042529 PCT/EP2010/065077 Initial activity 21100 MBq @12:00 Activity of formulated product 4880 MBq @13:28 =23% end of synthesis yield Radiochemcial purity was >99% two hours after the end of synthesis. Total cold ligand measured by was 3 tg/10 mL volume. This is calculated using analytical HPLC UV peak area with the cold reference compound as 5 calibrating standard. This automated synthesis method produced radiolabeled material with approximately 1 tg of cold impurities total. This automated process also gave consistent yields over a range of starting radioactivity levels. The results from four consecutive syntheses are shown below. Non decay Amount of Amount of Amount of corrected formulated Radiochemical cold ligand impurities EOS yield product (MBq) purity pg pg 18.22 72.7 >99 23.13 4880 >99 20.34 7220 >99 21.59 38 >99 0.6 -1.0 10 -26- WO 2011/042529 PCT/EP2010/065077 Example 5: Preparation of ortho-f 8 FIflumazenil tert-butyl ester from ortho-Nitromazenil tert-butyl ester (17) H 0 KOtBu N O N CO 2 H diethyl chlorophosphate I Htert-butyl isocyanoacetate 11% N N02 0 NO 2 O 1% 15 N 0 N 0 N OtBu N OtBu N N

NO

2 0 17 F 0 Example 5(i): Preparation of Nitro Isatoic Acid (15) 5 2,6-Dinitrobenzoic acid (0.5 g, 2.36 mmol) in ethanol (5 mL) was heated to 800C. Ammonium sulfide (40-48%in water) (0.36 mL, 2.36 mmol) was then added (the yellow solution became a bright orange suspension) the mixture was heated under reflux for 0.5 h. TLC (DCM 80%, MeOH 20%) showed a faint spot below the starting material. Ammonium sulfide (3.6 mL, 20.4 mmol) was added and the 10 mixture became a darker orange. This mixture was then heated under reflux for 1 h after which time TLC indicated that the reaction had gone to completion. The solvents were removed under reduced pressure and then the residue washed with methanol. The methanol solution was decanted off and evaporated to dryness to afford 2-nitro-6-amino benzoic acid as a orange solid. This was then purified 15 using flash chromatography (DCM 90%/MeOH 10% -> 20% MeOH over 60CV, 12 g column) to afford the desired material (0.2 g, 46%). 1H NMR (D 6 -DMSO) 5 3.16 (2H, s, NH 2 ), 6.80 (1 H, dd, J = 8 and 1 Hz, H 2 NCCH), 6.93 (1 H, dd, J = 8 and 1 Hz, CHCNO 2 ), 7.22 (1 H, dd, J = 8 and 8 Hz, CHCHCH). 2-nitro-6-amino benzoic acid (2.8 g, 15.4 mmol) was dissolved in dioxane (20 mL). -27- WO 2011/042529 PCT/EP2010/065077 Triphosgene (1.52 g, 5.1 mmol) was added. The mixture was then heated under reflux for 1 h. The mixture was then allowed to cool. The precipitate was then collected by filtration to give the isatoic anhydride in quantitative yield. 1H NMR (D 6 -DMSO) 6 7.33 (1 H, dd, J = 8 and 1 Hz, ArCH), 7.59 (1 H, dd, J = 8 5 and 1 Hz, ArCH), 7.89 (1 H, dd, J = 8 Hz, ArCH), 12.2 (1 H, br s, NH). Example 5(Ii): Preparation of 4-Methyl-6-nitro-3,4-dihvdro-1H benzo[el{1,47diazepine-2,5-dione (16) Nitro isatoic acid (15) (3.5 g, 16.8 mmol) and sarcosine (1.50 g, 16.8 mmol) was dissolved in DMSO (8 mL). The mixture was then placed in a preheated heating 10 mantle at 1500C. The mixture was then heated at this temperature for ca. 30 minutes; after which time the reaction mixture was poured into water (50 mL). The resulting brown precipitate was collected by filtration and triturated with ethyl acetate to afford a pale brown powder (0.9 g, 11 %). 1H NMR (300 MHz, DMSO-d 6 ): 5H 3.08 (3H, s, NCH 3 ), 4.16 (2H, br s, CH 2 ), 7.39 15 (1H, dd, J = 8.0 and 2.0 Hz, HNCCH), 7.66 (1H, dd, J = 8.0 and 8.0 Hz, CHCHCH), 7.72 (1 H, dd, J = 8.0 and 2.0 Hz, CHCNO 2 ), and 10.80 (1 H, brs, NH); 1C NMR (300 MHz, DMSO-d 6 ): 50 34.9 (NCH 3 ), 51.8 (NCH 2 ), 119.9 (CHQHCNH), 121.0 (Q-CO), 125.1 (CHCHCNO 2 ), 138.3 (QNH), 151.0 (Q-NO 2 ), 163.2 (Q=O), and 169.7 (0=O). 20 Example 5(iii): Preparation of ortho-Nitromazenil tert-butyl ester (17) Potassium tert-butoxide (0.37 g, 3.27 mmol) was added to intermediate 16 (0.7 g, 2.98 mmol) in THF (56 mL) at 00C. The mixture was then stirred at 00C for 20 min (during which time a bright yellow precipitate was observed) and then cooled to 350C. Diethyl chlorophosphate (0.67 g, 3.88 mmol, 0.56 mL) was added slowly. 25 The reaction was stirred at 00C for 30 min during which time mixture became slightly more yellow in colour. The reaction flask was cooled to -350C and solution of tert-butyl isocyanoacetate (0.46 g, 3.26 mmol, 0.48 mL) was added followed by potassium tert-butoxide (0.37 g, 3.27 mmol). The suspension was then left to stir -28- WO 2011/042529 PCT/EP2010/065077 at room temperature overnight. The reaction was quenched with aq NaHCO 3 (50 mL) and extracted with EtOAc (3 x 50 mL). The combined organic layers were dried over MgSO 4 , concentrated to afford brown oil. The crude material was purified by silica gel chromatography eluting with ethyl acetate (A): methanol (B) 5 (0-1% B, 100 g, 40 mL/min). 17 was obtained as a pale yellow solid (9 mg, 1%). 1H NMR (300 MHz, CDCI 3 ): 5 H 1 .64 (9H, s, C(CH3)3), 3.19 (3H, s, NCH 3 ), 4.52 (1 H, d, J = 15.0 Hz, CONCH 3 CH4Hb), 5.45 (1H, d, J = 15 Hz, CONCH 3 CHaHb), 7.64 (1H, dd, J = 9.0 and 3.0 Hz, NCCHCH), 7.73 (1H, dd, J = 9.0 and 9.0 Hz, NCCHCH), 7.93 (1 H, dd, J = 9.0 and 3.0 Hz, O 2 NCCHCHCH), and 7.94 (1 H, s, 10 NCHN). Example 5(iv): Radiofluorination of ortho-Nitromazenil tert-butyl ester (17) to Obtain ortho-(P 8 Fflumazenil tert-butyl ester Radiofluorination was done on a TRACERIab automated synthesis module (GE Healthcare). The [ F] fluoride was trapped on a pre-condtioned QMA cartridge 15 and then transferred to the reaction vessel using a solution of Kryptofix 2.2.2 (11 mg) in MeCN (2000 pL) and K 2

CO

3 (in 80 pL water, 1.7 mg) from vial 1. The solution was dried at 1000C for 10 minutes then 1200C for 20 minutes using nitrogen plus vacuum flow and then cooled to 500C. To the dried [ F]fluoride was added ortho-nitromazenil tert-butyl ester (17, 5 mg) 20 in DMF (1 mL) from vial 3. The reaction mixture was heated at 1300C for 30 min then it was cooled to 500C. The reaction mixture was diluted with 10 mM phosphoric acid (2.5 mL) from vial 5 and was transferred to the crude product tube. The crude product was then transferred onto the preparative HPLC loop manually. 25 Preparative HPLC gave a peak with retention time 13.5 minutes which was cut into the TRACERIab round bottomed flask containing water (12 mL). The prepartative HPLC system was fitted with a liquid flow scintillation counter. -29- WO 2011/042529 PCT/EP2010/065077 HPLC Column Phenomenex Prodigy ODS-prep 250xlOmm 10 p Solvent A = 10 mM phosphoric acid, B = MeCN, 30% B isocratic Flow rate 4 mL/min UV 254 nm Loop 5 mL Sensitivity 2000K The mixture in the round bottom flask was trapped on a C18 lite SPE (pre conditioned with 1 mL ethanol then 2 mL water). The SPE was washed with water (3 mL) and the crude product eluted into a P6 vial using EtOH (0.5 mL) and 5 phosphate buffered saline (4.5 mL). The product was further diluted using phosphate buffered saline to give a final volume of 10 mL. Initial activity 828 MBq @9:59 Activity of formulated product 121 MBq @11:51 =14.6% end of synthesis yield Radiochemcial purity was >99% two hours after the end of synthesis. 10 Total cold ligand measured by was 6 tg/1 0 mL volume (calculated using analytical HPLC UV peak area with the cold reference compound as calibrating standard). 15 -30- WO 2011/042529 PCT/EP2010/065077 Example 6: Radiofluorination of ortho-Nitromazenil isopropyl ester (18) to Obtain ortho- 8 Flflumazenil isopropyl ester N O'- N O N 0 Isopropanol Ti(O-i-Pr) 4 N N N

NO

2 O

NO

2 O 14 18 Example 6(i): Preparation of ortho-Nitromazenil isopropv ester (18) 5 14 (preparation described in Example 4(iii); 20 mg, 0.06 mmol) was dissolved in 2 mL of isopropanol in a microwave vessel and 50 tl of Titanium (IV) isopropoxide were added. Microwave conditions: Temperature: 850C; Time: 60 mins. LCMS confirmed quantitative conversion of the starting material to the desired product. This was also confirmed by TLC using ethyl acetate. The excess isopropanol was 10 removed to dryness and the crude mixture was liquid loaded on column for flash chromatography using petrol and ethyl acetate as eluent. The material was purified again using DCM/Methanol. 18 (15 mg) was obtained pure (73%). 1H NMR (CDC1 3 ) 5 1.43 (3H, d, J = 6.1 Hz, CH3), 1.45 (3H, d, J = 6.1 Hz, CH3), 3.20 (3H, s, NCH 3 ), 4.53 (1H, d, J= 16Hz, CH), 5.28 (1H, d, J= 16 Hz, CH'), 5.33 15 (1H, m, COOCH(CH 3

)

2 ), 7.66 (1H, dd, J= 0.92, 8.27 Hz, CHCHCHCNO 2 ), 7.75 (1H, t, J = 8.3 Hz, CHCHCHCNO 2 ), 7.94 (1H, dd, J = 0.92, 8.27 Hz,

CHCHCHCNO

2 ), 7.97 (1 H, s, NCHN). Example 6(ii): Radiofluoriantion of ortho-Nitromazenil isopropvl ester (18)to Obtain ortho-(P 8 Flflumazenil isopropvl ester 20 Radiofluorination was done on a TRACERIab automated synthesis module (GE Healthcare). The [ F] fluoride was trapped on a pre-condtioned QMA cartridge and then transferred to the reaction vessel using a solution of Kryptofix 2.2.2 (11 mg) in MeCN (2000 pL) and K 2

CO

3 (in 80 pL water, 1.7 mg) from vial 1. The solution was dried at 1000C for 10 minutes then 1200C for 20 minutes using -31- WO 2011/042529 PCT/EP2010/065077 nitrogen plus vacuum flow and then cooled to 500C. To the dried [ F]fluoride was added ortho-nitromazenil tert-butyl ester (2.5 mg) in DMF (1 mL) from vial 3. The reaction mixture was heated at 1300C for 30 min then it was cooled to 500C. The reaction mixture was diluted with 10 mM phosphoric 5 acid (2.5 mL) from vial 5 and was transferred to the crude product tube. The crude product was then transferred onto the preparative HPLC loop manually. Preparative HPLC gave a peak with retention time 23 minutes which was cut into the TRACERIab round bottomed flask containing water (15 mL). The prepartative HPLC system was fitted with a liquid flow scintillation counter. HPLC Column Phenomenex Prodigy ODS-prep 250x10mm 10 p Solvent A = 10 mM phosphoric acid, B = MeCN, 25% B isocratic Flow rate 4 mL/min UV 254 nm Loop 5 mL Sensitivity 2000K 10 The mixture in the round bottom flask was trapped on a C18 lite SPE (pre conditioned with 1 mL ethanol then 2 mL water). The SPE was washed with water (3 mL) and the crude product eluted into a P6 vial using EtOH (0.8 mL) and phosphate buffered saline (7.2 mL). 15 Initial activity 800 MBq @10:51 Activity of formulated product 114 MBq @12:56 =14.2% end of synthesis yield Radiochemcial purity was >99% three hours after the end of synthesis. -32- WO 2011/042529 PCT/EP2010/065077 Total cold ligand measured by was 2.4 ptg/8 mL volume (calculated using analytical HPLC UV peak area with the cold reference compound as calibrating standard). Total cold impurities were approximately 2 tg. Example 7: In Vivo Biodistribution of ortho-f 8 F1-flumazenil 5 Adult male Sprague-Dawley rats (body weight 202±37 g; mean ±SD) were injected with between 1 and 5 MBq of ortho-[ F]-flumazenil via a lateral tail vein. All animals were conscious, but lightly restrained during injection and subsequently housed in short-term metabolism cages. At the appropriate time point; 30 seconds, 2, 10, 30 and 60 minutes post-injection (pi) (n=3 per time 10 point), the animals were sacrificed by cervical dislocation. The brain and peripheral tissues or fluids were sampled post-mortem. Radioactivity in the brain samples was measured using a Wallac gamma counter. Once assayed, the brain samples, along with the remaining organ or tissue samples were assayed using a twin-crystal gamma-counter system (BASIL), with automatic 15 correction for radioactive decay. The table below shows the data obtained in the brain regions. Data is expressed as mean (±SD), and all are n=3. Data indicated by an asterisk (*) is % id/g. Distribution of ortho-[ 18 F]-flumazenil Time Post-injection [minutes (standard deviation) 0.5 2 10 30 60 Brain Region (% idlg) Striatum 0.90 (0.02) 0.83 (0.22) 0.68 (0.08) 0.15 (0.02) 0.06 (0.03) Cerebellum 0.99 (0.08) 1.01 (0.28) 0.96 (0.07) 0.38 (0.08) 0.11 (0.02) Hippocampus 0.81 (0.04) 0.78 (0.25) 0.91 (0.06) 0.48 (0.10) 0.17 (0.01) Pre-frontal cortex 1.12 0.03) 1.14 (0.28) 1.39 (0.06) 0.76 (0.20) 0.29 (0.04) Thalamus 1.03(0.18) 0.85(0.29) 0.94(0.15) 0.33(0.07) 0.08 0.02) Pituitary gland 0.98 (0.14) 1.12 (0.31) 0.46 (0.08) 0.15 (0.09) 0.02 0.01) Pons/Medulla 0.79 (0.03) 0.79 (0.22) 0.59 (0.05) 0.21 (0.15) 0.24 (0.38) Pre-frontal cortex:thalmus 1.11 1.37 1.50 2.28 3.96 -33- WO 2011/042529 PCT/EP2010/065077 Initial uptake of radioactivity in the brain was 1.4±0.8% id after 30 seconds pi, peaking at 1.8±0.5% id at 2 minutes pi. After 2 minutes pi there was a steady decrease in radioactivity levels, with 0.9±0.2% id after 30 minutes pi falling to 5 0.3±0. 1% id by 60 minutes pi. The region with the highest levels of radioactivity at the early time points was the pre-frontal cortex (1.39±0.06% id at 10 minutes pi). There was good differentiation between the GABA-rich and GABA-poor regions to 30 min pi. -34-

Claims (1)

1. 6-10; and 15 (ii) means for eluting the vessel with a suitable source of [1 F]Fluoride, wherein said suitable source of [1 F]Fluoride is as defined in any one of Claims 1, 11 or 12. 16)The cassette as defined in Claim 15 which additionally comprises an ion exchange cartridge for removal of excess [1 F]Fluoride. 20 17)A compound of Formula I as defined in the method of Claim 1 wherein R 1 is hydrogen, R 2 is 18 F, and R 4 is ethyl, isopropyl or tert-butyl. 18)A precursor compound of Formula la as defined in the method of Claim 1 wherein one of R" and R is trimethylammonium or -I*-Ar, and the other is hydrogen. 25 19)The precursor compound as defined in Claim 18 wherein one of R" and R1 is -37- WO 2011/042529 PCT/EP2010/065077 trimethylammonium and the other is hydrogen. 20)A precursor compound of Formula la as defined in the method of Claim 1 wherein R is nitro, trimethylammonium or -I*-Ar. 21)The precursor compound as defined in Claim 20 wherein R is nitro. 5 22)The precursor compound as defined in any one of Claims 18-21 wherein R 13 is C(=O)-O-R 4 wherein R 4 is ethyl, isopropyl or tert-butyl. -38-